This invention relates to control systems for torque converters, and more particularly, to pressure control systems for torque converter and clutch assemblies.
Specifically, this invention relates to a valve arrangement for controlling the outlet pressure of a torque converter and clutch assembly in a 3-path control circuit.
Torque converter and clutch assemblies use either a 2-path or 3-path control circuit. In a 2-path control circuit, one passage or path is pressurized for clutch apply while the other is exhausted. For clutch release, the function of the passages is reversed.
In a 3-path system, one path or passage is always the torque converter outlet passage. One passage is always a clutch apply passage and is always pressurized while the remaining passage, a clutch release passage, is selectively pressurized to control the operating condition of the clutch. In these 3-path prior art systems, the same amount of fluid flows through the torque converter (from apply to outlet) regardless of the operating condition of the clutch.
As a general rule, the volume of required fluid flow through the torque converter is determined by the heat to be rejected. Thus, during torque converter operation, large flow volumes are desired, particularly at stall conditions. However, when the torque converter clutch is engaged, the torque converter does not generate heat and less fluid flow is required.
The 2-path system accommodates this changing requirement by switching the input flow part to the converter and connection the outlet to the cooler. During clutch engagement, the flow through the torque converter is restricted by the clutch structure, thus reducing the flow through the torque converter. A 3-path system does not have this advantage and accordingly has higher than required fluid flow, through the torque converter, during clutch engagement. This reduces the overall efficiency of the system.